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The amorphous oxide thin-film transistor (TFT)-oriented simulator [subgap Density of states (DOS)-based Amorphous Oxide TFT Simulator (DeAOTS)] is proposed, implemented, and demonstrated for amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs. It only consists of parameters having their physical meanings and is supplied with concrete techniques for parameter extraction. Among the physical parameters, the acceptor-like DOS gA(E) was experimentally extracted using the multifrequency C-V technique, whereas the donor-like DOS gD(E) and the doping concentration ND were extracted using numerical iterations. The simulation result reproduces the DOS and thin-film-thickness-dependence of dc I-V characteristics very well. Compared with the previously reported a-Si TFT models, the proposed DeAOTS model not only reflects the strong VGS dependence of the effective mobility (μeff) but also clarifies the relations between process-controlled DOS parameters and dc I- V characteristics based on experimentally extracted DOS parameters. Also, it sufficiently takes into account the peculiar situation of amorphous oxide TFTs where the free-carrier charge can be larger than the localized one out of the total induced charge. Moreover, it reproduces the measured electrical characteristics within the wide range of VGS/VDS with a single equation, not distinguishing the operation regions such as the subthreshold, linear, and saturation regimes.